NATURE 
57 
THURSDAY, SEPTEMBER 18, 10913. 
THE STRUCTURE OF THE ATMOSPHERE 
: IN CLEAR WEATHER. 
The Structure of the Atmosphere in Clear 
Weather: a Study of Soundings with Pilot 
_ Balloons. By C. J. P. Cave, M.A. Pp. xii+144. 
(Cambridge : The University Press, 1912.) Price 
Ios. 6d. net. 
R. CAVE’S book is a welcome addition to 
4 the valuable contributions of amateurs to 
the common stock of scientific knowledge, and is 
“the more welcome as the first book on this special 
_ Subject. The investigation of the upper air is of 
“Such interest and the incidental problems which it 
_ presents are so numerous, so attractive, and, in 
hese days of flying, so practical, that it is a matter 
of some surprise that there are not found more men 
of leisure to follow the notable examples of Prof. 
_ Lawrence Rotch and M. Teisserenc de Bort in the 
_ investigation of the free atmosphere. Mr. Cave in 
his introduction refers to the circumstances in 
which he began the study of the subject. As a 
matter of history, they can be traced to a letter 
_by the present writer in The Times asking for the 
cooperation of yachtsmen in the exploration of the 
air over the sea by means of kites. Since that 
letter appeared we have had to chronicle the divi- 
sion of the atmosphere into two distinct layers, an 
upper layer,.the stratosphere, in which there is 
little or no variation of temperature in the vertical, 
but sensible variation from day to day, or along 
the horizontal, and a lower layer, the troposphere, 
in which the variation of temperature is greatest 
in the vertical and relatively small along the hori- 
zontal. At the boundary between the two layers 
which is found at different heights in different 
regions, and on different occasions according to the 
barometric pressure, there is generally a slight 
‘inversion in the fall of temperature with 
height. Ten kilometres may be taken as a rough 
and ready estimate of the average thickness of the 
troposphere with the understanding that there is a 
latitude of three or more kilometres to be allowed 
in either direction according to circumstances. 
With the progress of the general investigation 
of the upper air attention has been directed especi- 
ally to the observation of air-currents at different 
levels by means of pilot balloons watched through 
theodolite-telescopes of special construction, intro- 
‘duced by M. de Quervain. Mr. Cave’s book gives 
a comprehensive account of the methods and re- 
‘sults of work of this character based upon his own 
€xperience at Ditcham Park and elsewhere. The 
apparatus is simple and less expensive than that 
required for the determination of temperatures :— 
NO. 2290, VOL. 92] 
a balloon which need not be large enough to 
carry recording instruments, some hydrogen, and 
accessories, two theodolites to be used simultane- 
ously from two ends of a base for the observation 
of the altitude and azimuth of the rising balloon 
at the end of each minute or half minute from the 
start. One of the theodolites may be dispensed 
‘with if the observer knows with reasonable accu- 
racy the rate of ascent of the balloon, and, as 
appears from one of Mr. Cave’s chapters, this 
condition may be assumed without fear of losing 
the characteristic features of the ascent. In fact, 
observations of pilot balloons with one theodolite 
have been asked for as part of an international 
enterprise. The reduction of the observations is 
laborious, as each sounding entails the solution of 
many triangles, but with the judicious use of a 
slide rule and tables as described on p. 12, the 
labour is apparently not intolerable. The results 
of two hundred soundings in 1907, 1908, and 
1909, with one in 1910 involving the solution of 
8000 triangles, are given in the book. They are 
classified according to certain types of structure. 
For each sounding the velocity and direction of 
the horizontal motion of the air at each half kilo- 
metre are given in tables on pp. 84—107, and they 
are illustrated by a number of diagrams showing 
the variation of direction and velocity with height, 
accompanied by the weather maps which represent 
the distribution of surface pressure on the occa- 
sions of the ascents. A word of praise must here 
be given for the excellence of the arrangement 
and printing of the tables and of the diagrams 
and maps. 
The order of the book also deserves remark. 
Mr, Cave has departed from the usual course in 
not taking the mean values of all the fish that 
have come into his net. He has sorted out his 
catch before submitting it to digestion. In fact, 
there are, if we recollect rightly, no mean values 
anywhere in the book. In the present state of our 
knowledge this decision is a wise one, for until 
the variations are reduced to those of observation 
alone, a mean value often conceals more truth 
than it reveals, and is sometimes actually mis- 
leading. 
The first step in the discussion is to form a 
selection of types of structure. These are excel- 
lently illustrated by photographs of cardboard 
models. 
The use of pilot balloons is subject to some 
obvious limitations. There is no little difficulty in 
pursuing a balloon with a theodolite for great 
distances. On one favourable occasion Mr. Cave 
kept a balloon in view until it was forty miles 
away, but ordinarily a sounding comes to an end 
by losing sight of the small speck in the field of 
D 
